Polytrimethylene terephtalate conjugate fiber and method of preparing the same

ABSTRACT

Disclosed is a polytrimethylene terephtalate conjugate fiber having high self-crimpability, which is prepared by conjugate-spinning two types of polytrimethylene terephtalates having different intrinsic viscosities in which a difference between the intrinsic viscosities ranges from 0.05 to 0.15 into a side-by-side fiber. Also, the polytrimethylene terephtalate conjugate fiber prepared by the conjugate-spinning undergoes a false twisting process, leading to development of three-dimensional high self crimpability and sufficient bulky property in the resulting fiber.

TECHNICAL FIELD

The present invention, in general, relates to a polyester conjugate fibers and method of preparing such fibers. In detail, the present invention relates to a polyester conjugate fiber, and a method of preparing such a fiber, comprising conjugate-spinning two types of polyesters having different intrinsic viscosities to produce a fiber having a side-by-side cross-section, and subsequently performing a heat-treating and relaxation process to develop high self-crimpability and overall quality of the fiber. More particularly, the present invention relates to a method of preparing a polyester conjugate fiber, capable of developing crimpability and supplying good spinning operability even at a smaller difference between intrinsic viscosities of two polymers than a conventional intrinsic viscosity difference.

BACKGROUND ART

Several methods of preparing side-by-side conjugate fibers are conventionally known. As representative examples, one is to prepare such conjugate fibers by conjugate-spinning a polyester and its copolymer having high shrinkability to produce a side-by-side fiber, and the other is to prepare conjugate fibers by conjugate-spinning two different polyesters to produce a side-by-side fiber. However, such methods are disadvantageous in that copolymers typically have deteriorated physical properties and poor spinning operability, and resulting fibers have a limited crimping level. The above two methods are for preparation of flat yarns by a spin-draw process. Flat yarns prepared by the conventional methods have a crimping rate of about 30% (when measured by the method provided in the present invention), thus providing elasticity to manufactured textile fabrics. However, additional fabric weave patterns should be designed to develop high elasticity, and it is especially hard to obtain satisfactory elasticity in fabric weaves having many cross-links of warp and weft.

As another example of a conjugate spinning method using the difference between intrinsic viscosities of two polymers, Japanese Pat. Laid-open Publication No. 2000-256918 discloses a latent crimp polyester conjugate fiber, which is prepared by conjugate-spinning polyester ‘A’ containing trimethylene terephtalate at an amount of over 85 mol % of repeat units and an uncopolymerized component having three or more ester-forming functional groups, and either of polyester ‘B’ containing trimethylene terephtalate at an amount of over 85 mol % of repeat units and a component having three or more ester-forming functional groups at an amount of 0.5-0.2 mol %, and polyester ‘C’ containing trimethylene terephtalate at an amount of over 85 mol % of repeat units and an uncopolymerized component having three or more ester-forming functional groups, having an intrinsic viscosity lower than the polyester ‘A’ by 0.15-0.30, into a side-by-side or eccentric sheath-core type fiber. To develop crimpability of such a conjugate fiber, two polyester components must have a difference of over 0.15 in their intrinsic viscosities. Also, since crimp is not easily developed in a flat yarn form, the fiber in the flat yarn form must be processed into a false twisted yarn by a false twisting treatment to obtain desired crimpability. Owing to such a difference in intrinsic viscosities, the fiber is severely curved at a lower part of a spinning nozzle, and spinning operability is very poor. Especially, in the case that the difference in intrinsic viscosities of two components of a side-by-side fiber is small good spinning operability is obtainable, but it is hard to develop crimpability in a resulting fiber.

DISCLOSURE OF THE INVENTION

Therefore, it is an object of the present invention to provide a polyester conjugate fiber of a side-by-side type, not having the aforementioned disadvantages.

Leading to the present invention, the intensive and thorough research into a polyester conjugate fiber, conducted by the present inventors with an aim to achieve the above object, resulted in the finding that a conjugate fiber can be prepared by conjugate spinning two different types of trimethylene terephtalates having a difference of 0.05-0.15 in their intrinsic viscosities into a side-by-side fiber, with good spinning operabililty, and the resulting conjugate fiber exhibits high self-crimpability even in a flat yarn form, not in a false twist yarn form, in addition that, when a bicomponent conjugate fiber prepared by conjugate-spinning polymers having a small difference between their intrinsic viscosities is subjected to a false twisting treatment, difference in shrinkage of the polymers occurs owing to the difference in the intrinsic viscosities of the polymers, and latent torque is developed by false twisting at a heat treatment step, thereby giving a conjugate fiber with high crimpability as well as sufficient bulky property.

BRIEF DESCRIPTION OF DRAWINGS

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates an example of a cross-section of polytrimethylene terephtalate conjugate fibers prepared according to the present invention; and

FIG. 2 is a schematic view of a spinning machine equipped with extruders, which is used to produce the fibers of Examples of the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION

In accordance with the present invention, there is provided a method of preparing a polytrimethylene terephtalate conjugate fiber, comprising conjugate spinning two types of polytrimethylene terephtalates having different intrinsic viscosities into a side-by-side fiber in which a difference between the intrinsic viscosities ranges from 0.05 to 0.15, under a condition, which achieves a difference between melt viscosities of the two polymers in a range of below 1000 poise.

In addition, the present invention provides a polytrimethylene terephtalate conjugate fiber comprising two types of polytrimethylene terephtalates having different intrinsic viscosities, where a difference between the intrinsic viscosities ranges from 0.05 to 0.15, and having a side-by-side structure.

The two types of polytrimethylene terephtalates conjugate-spun into a side-by-side fiber according to the present invention have different intrinsic viscosities in which the difference between the intrinsic viscosities is preferably in a range of from 0.05 to 0.15. When the difference between the intrinsic viscosities is adjusted to a narrow range of from 0.05 to 0.15 to make a difference between melt viscosities of the two polymers below 1000 poise, a side-by-side fiber having a structure shown as in FIG. 1 can be melt-spun without additional nozzle designs and has good spinning operability, in addition that a desired fiber having good crimpability can be obtained just by combination of two polymers having a small difference in intrinsic viscosity by suitably setting temperatures of extruders.

Hereinafter, a polytrimethylene terephtalate having a high intrinsic viscosity is referred to as “PTT-H”, and a polytrimethylene terephtalate having a low intrinsic viscosity is referred to as “PTT-L”. PTT-H and PTT-L used for preparation of a polytrimethylene terephtalate conjugate fiber of the present invention, which contain terephtalate and propandiol as major components, preferably contain unpolymerized trifunctional ester-forming components. Herein, bis(3-hydroxypropyl)ether (DPG) and cyclic dimmer as by-products generated during polymerization may be present at amounts of less than 3.0 mol %/diol and less than 3 wt %, respectively. Generally, when the difference between intrinsic viscosities of PTT-H and PTT-L is below 0.15, it is known that a difference between shrinkages of the two polymers is small owing to a small difference between melt viscosities between the two polymers, thereby not producing a desired fiber having a satisfactory crimping rate. In accordance with the present invention, when the difference between melt viscosities of the two polymers and their combination ratio are regulated, a polytrimethylene terephtalate conjugate fiber having a desired crimping rate is prepared even by using polymers having the same viscosity difference described above. When the difference between the melt viscosities of the two polymers is below 1000 poise, and more preferably less than 300 poise, a resulting fiber having a satisfactory crimping rate of over 30% even may be obtained using the polymers having the small viscosity difference of below 0.15. A method of measuring the crimping rate will be described below, and the crimping rate should be over 30% to manufacture a fabric having sufficient elasticity.

The difference between the melt viscosities of the two polymers may be regulated by extruding the two polymers at different temperatures to generate different heat histories in melted products of the two polymers, or modifying combination ratio of a polymer having high viscosity and a polymer having low viscosity. To adjust the difference between the melt viscosities of PTT-H and PTT-L to be below 1000 poise, spinning temperature is preferably in a range of from 235 to 275° C.

In accordance with the present invention, PTT-H and PTT-L have different intrinsic viscosities ranging from 0.7 to 1.1, and the difference between the intrinsic viscosities of the two polymers is preferably from 0.05 to 0.15. When the intrinsic viscosity of each polymer is less than 0.7 or more than 1.1, spinning operability is poor. Especially, the ‘K’ value calculated according to Equation 1, below, is preferably in a range of 0<K≦0.09. K={[η] _(H)-[η]_(L)}/{[η]_(H)+[η]_(L)}  [Equation 1]

-   -   wherein, [η]_(H) is an intrinsic viscosity of PTT-H, and [η]_(L)         is an intrinsic viscosity of PTT-L.

Preferably, PTT-L has an intrinsic viscosity of 0.8-0.95 and is 30-70% of total weight of a resulting fiber, and PTT-H has an intrinsic viscosity of 0.85-1.1 and is 70-30% of total weight of the resulting fiber.

When spinning the two polymers at a melt viscosity difference of below 1000 poise, a side-by-side fiber having a crimping rate of 30% is obtained. Such a fiber is usable to prepare elastic fabrics, but not suitable for preparation of high elastic fabrics that are manufactured using spandex covered yarns and require high crimping rate. In accordance with the present invention, a crimped flat yarn is prepared and then undergoes a false twisting process, thereby producing a grey yarn usable in preparing highly elastic fabrics.

The spinning speed suitable in the present invention is preferably set to, but is not limited to, 1,500-4,000 m/min. In addition, in order to obtain a highly elastic conjugate fiber having three-dimensional crimp by false twisting the flat yarns prepared at the spinning speed, a false twisting-draw ratio and a false twisting temperature are important. The false twisting-draw ratio is preferably from 1.0 to 1.5, and the false twisting temperature is preferably from 100 to 180° C.

When a drawing process is carried out at a draw ratio of 1.0-1.5, simultaneously with false twisting, using a false twister comprising a first feed roller (first FR), a heater, a cooling plate, a friction twisting apparatus and a second feed roller (second FR), in which each component is arranged in order of steps of processing a yarn, it is preferable that drawing is performed between the first FR and the second FR at a drawing rate of 1.0-1.5. In such a case, the yarn is false-twisted at the upstream region of the friction twisting apparatus, and is thermal-fixed by the heater, and the shape of the yarn is fixed by the cooling plate. The false twisting-draw ratio is preferably from 1.00 to 1.50, and more preferably, 1.03 to 1.20. When the false twisting-draw ratio is below 1.0, a suitable false twist tension is hard to maintain and thus work operability is poor, and high crimpability is not obtained. When the false twisting-draw ratio exceeds 1.5 and fine naps and yarn cutting are increased, causing bad workability. A friction twisting apparatus useful in the present invention includes inscribed or circumscribed-type friction twisting apparatuses capable of acting to twist as well as feed, and preferably, a circumscribed-type shaft twister and a belt nip twister. The draw ratio is determined depending on physical properties of a polytrimethylene terephtalate undrawn yarn or false twisted yarn, wherein a residual elongation is preferably 30-65%, and more preferably, 35-50%.

In order to enhance crimpability of false twisted yarns and thus improve stretching property and bulky property of fabrics, the false twisting temperature of the yarns at an outlet of the heater during the false twist-drawing process is preferably from 100 to 180° C. When the false twisting temperature is below 100° C., quality of fabrics is deteriorated, as follows: false twist tension is increased, thus leading to increased generation of yarn cutting and crimps are not suitably generated during the false twisting process, dimensional stability or crimpability is reduced, and shrinkage difference is induced at a heat-treating process performed as a post-process after preparation of false twisted yarns and thus color change occurs in fabrics. When the false twisting temperature is over 180° C., thick regions of the yarns remain in a twisted form, thus deteriorating their quality, and melt-integration of the yarns occurs and thus three-dimensional crimp cannot be obtained and workability is poor. The flat yarns prepared by the above false twisting process have latent torque, and the latent torque is developed by a relaxation heat-treatment performed as a post-process, thereby producing a final conjugate fiber having good crimpability, bulky property and abundant crimps.

In accordance with the present invention, there is provided a polytrimethylene terephtalate conjugate fiber, which comprises two types of polytrimethylene terephtalates having different intrinsic viscosities in which a difference between the intrinsic viscosities ranges from 0.05 to 0.15. The resulting conjugate fiber has a side-by-side structure, a strength of 2.0-3.5 g/den, an elongation of 30-65%, a crimping rate of over 20% and an elastic recovery of over 90% at an elongation of 30%. When the strength is below 2.0 g/den, yarn cutting often occurs owing to the low strength, and workability in manufacturing fabrics is bad. When the strength is over 3.5 g/den, texture of fabrics is bad. Also, when the elongation is below 30%, a lot of fine naps are generated on the resulting yarns during spinning. When the elongation is over 65%, uniformity in fiber size (U %) is deteriorated When the crimping rate is below 30%, desired elasticity is hard to obtain. When the elastic recovery at an elongation of 30% is below 90%, elastic recovery is not good and thus clothing is uncomfortable, and the ability of the yarns to restore their original state is lowered owing to repeated deformation and frictional damage to the yarns, causing the initial shapes of clothes to be lost.

The present invention will be explained in more detail with reference to the following an example in conjunction with the accompanying drawings. However, the following example is provided only to illustrate the present invention, and the present invention is not limited to the example.

EXAMPLE 1

Using an extruder equipped with a spinning device as shown in FIG. 2, polytrimethylene terephtalate having an intrinsic viscosity (IV) of 1.0 at an amount of 50% by weight, which was used as PTT-H, and polytrimethylene terephtalate having an IV of 0.9 as PTT-L were spun at a spinning speed of 2000 m/min and at extruder temperatures of 260° C. and 265° C., respectively, using a side-by-side-type spinning nozzle, and then drawn at a draw ratio of 1.5, a draw temperature of 55° C. and a heat treatment temperature of 220° C. Cool air of 23° C. was supplied at a speed of 0.3 m/sec to a position of 5-120 cm under the nozzle, and oil pickup (OPU) was determined to 0.5 to 1.0 wt %. Using resulting fibers as warps and wefts, a woven fabric of weight of 100 g/m² was processed and then stained at 105° C. A difference between intrinsic viscosities of the two polymers, PTT-H and PTT-L, was 0.1, and the ‘K’ value was 0.053.

EXAMPLES 2 TO 4

Woven fabrics were prepared and stained according to the method as in Example 1 except for change of extruder temperatures of polytrimethylene terephtalate having an IV of 1.0 as PTT-H and polytrimethylene terephtalate having an IV of 0.9 as PTT-L to temperatures as listed in Table 1, below.

EXAMPLES 5 TO 10

PTT-H and PTT-L having intrinsic viscosities and various combination ratios as shown in Table 2, below, were spun at a speed of 2000 m/min and at a spinning beam temperture of 265° C. using a side-by-side-type spinning nozzle, drawn at a draw ratio of 1.5, a draw temperature of 60° C. and a heat treatment temperature of 200° C.

EXAMPLES 11 TO 16

Using the a spinning machine equipped with extruders, 50 wt % of polytrimethylene terephtalate having an intrinsic viscosity (IV) of 1.0 as PTT-H, and 50 wt % of polytrimethylene terephtalate having an IV of 0.9 as PTT-L were spun at a spinning speed of 3,500 m/min at a spinning beam temperature of 265° C. using a side-by-side-type spinning nozzle, thus preparing flat yarns. Cool air of 23° C. was supplied at a speed of 0.3 m/sec to a position of 5-120 cm under the nozzle, and oil pickup (OPU) was determined to 0.4 to 0.8 wt %. The resulting yarns were drawn with false twisting at various false twisting temperatures and various draw ratios as shown in Table 3, below, using a false twister (Murata 33H), thus producing false twist fibers. Using the fibers as warps and wefts, woven fabrics of weight of 200 g/m² were produced, and then stained at 105° C. A difference between intrinsic viscosities of the two polymers was 0.1, and the ‘K’ value was 0.053. Physical properties of the polymers and fibers were evaluated by the following methods.

Intrinsic viscosity (IV): After sufficiently dissolving each polymer in a 1% ortho-chloro phenol solution of 120° C., intrinsic viscosity was measured at a water bath of 30° C. using an Ubbelohde viscometer.

Crimping rate (TC, %): Under a tension of 50 mg/de, a sample of a bundle of yarns of 3000 de was obtained. The sample was heat-treated in hot water of 100° C. for 20 min under a load of 0.5 mg/de not causing tangling of yarns, whereby crimp is developed. After removing the load, the sample was cooled for 4 hrs and air-dried. 1 min after supplying a load of 2 mg/de to the air-dried sample, length L₁ of the yarns was measured. After measuring L₁, a load of 2 mg/de+200 mg/de was applied to the sample, and, after 1 min., length L₂ of the yarns was measured. The crimping rate (TC) was calculated according to Equation 2, below, using the measured L₁ and L₂ values.

TC(%)={(L ₂ −L ₁)/L ₂}×100  [Equation 2]

Elastic recovery of a resulting fabric at an elongation of 30% (FR₃₀, %): Three fabrics of 5.5 cm×30 cm (warp×weft) were produced. A test piece 5 cm wide was placed in a tension tester, and an initial load was applied to spread out the test piece. The test piece was elongated to an elongation of 30% at a speed of 100%/min according to a low speed elongation measuring method (JIS L 1018-70). Thereafter, the test piece was restored at the same speed in a reverse direction. An elongation (ε) was estimated when a stress reaches initial load stress at a stress-elongation curve, and an average elongation at each warp and weft direction was calculated, and then FR₃₀ was calculated according to Equation 3, below. FR ₃₀(%)={(30−ε)/30}×100  [Equation 3] TABLE 1 Extruder temp. (° C.) Spinning Examples PTT-H PTT-L beam temp. (° C.) K values 1 260 265 265 0.053 2 255 265 265 0.053 3 250 265 265 0.053 4 265 260 265 0.053

TABLE 2 PTT-H Ratio PTT-L Examples IV (wt %) IV Ratio (wt %) IV difference K values 5 1.0 50 0.90 50 0.10 0.053 6 1.0 50 0.85 50 0.15 0.008 7 1.0 55 0.90 45 0.10 0.053 8 1.0 60 0.90 40 0.10 0.053 9 1.0 70 0.90 30 0.10 0.053 0 1.0 40 0.90 60 0.10 0.053

TABLE 3 Spinning beam False twisting- Draw Examples temp. (° C.) K values draw ratio temp. (° C.) 11 265 0.053 1.1 120 12 265 0.053 1.1 140 13 265 0.053 1.1 160 14 265 0.053 1.05 160 15 265 0.053 1.10 160 16 265 0.053 1.20 160

Physical properties and crimping rates (TC) of the conjugate fibers prepared in the above Examples are summarized in Table 4, below. TABLE 4 Examples Strength (g/de) Elongation (%) TC (%) FR₃₀ (%) 1 2.92 52.4 37.2 96 2 2.89 53.7 38.4 97 3 2.86 55.7 42.3 97.5 4 2.84 53.7 32.3 94 5 2.91 53.3 36.4 96 6 2.81 55.7 42.4 98 7 2.83 54.2 37.4 97 8 2.84 53.7 41.3 98 9 2.84 54.2 43.2 98.4 10 2.80 56.4 32.4 94 11 2.69 53.4 53.4 98.1 12 2.77 55.9 61.9 98.4 13 2.71 52.6 70.0 99.1 14 2.69 54.4 59.3 98.4 15 2.71 52.6 70.0 99.1 16 2.74 51.2 72.0 99.3

INDUSTRIAL APPLICABILITY

As apparent from the data of the above Examples, in accordance with the present invention, when spinning two different polytrimethylene terephtalates having a low intrinsic viscosity difference under a melt viscosity difference of below 1000 poise, a polyester conjugate fiber having self-crimpability in a flat yarn form, not in a false twist fiber, can be prepared. In addition, by additionally false twisting the flat yarn, a polyester conjugate fiber showing high crimpability and bulky property by induced latent torque can be prepared, supplying good spin-draw operability. 

1. A method of preparing a polytrimethylene terephtalate conjugate fiber, comprising conjugate spinning two types of polytrimethylene terephtalates having different intrinsic viscosities into a side-by-side fiber in which a difference between the intrinsic viscosities ranges from 0.05 to 0.15, under a condition to achieve a difference between melt viscosities of the two polymers in a range of below 1000 poise.
 2. The method as set forth in claim 1, wherein the two types of polytrimethylene terephtalates comprise a polytrimethylene terephtalate (PTT-H) having high intrinsic viscosity and a polytrimethylene terephtalate (PTT-L) having low intrinsic viscosity, said PTT-H and PTT-L having different intrinsic viscosities in a range of from 0.7 to 1.1.
 3. The method as set forth in claim 1, wherein the two types of polytrimethylene terephtalates comprise a polytrimethylene terephtalate (PTT-H) having high intrinsic viscosity and a polytrimethylene terephtalate (PTT-L) having low intrinsic viscosity, said PTT-H and PTT-L satisfying a ‘K’ value of 0<K≦0.09, calculated according to the following Equation: K={[η] _(H)−[η]_(L)}/{[η]_(H)+[η]_(L)}wherein, [η]_(H) is the intrinsic viscosity of PTT-H, and [η]_(L) is the intrinsic viscosity of PTT-L.
 4. The method as set forth in claim 1, wherein the two types of polytrimethylene terephtalates comprise a polytrimethylene terephtalate (PTT-H) having high intrinsic viscosity and a polytrimethylene terephtalate (PTT-L) having low intrinsic viscosity, and content of said PTT-H is 30-70% of total weight of the conjugate fiber and content of said PTT-L is 70-30% of total weight of the conjugate fiber.
 5. The method as set forth in claim 1, wherein the two types of polytrimethylene terephtalates comprise a polytrimethylene terephtalate (PTT-H) having high intrinsic viscosity and a polytrimethylene terephtalate (PTT-L) having low intrinsic viscosity, and spinning temperature of the PTT-H and PTT-L is in a range of from 235 to 275° C.
 6. The method as set forth in claim 1, wherein the polytrimethylene terephtalates are conjugate-spun into a side-by-side fiber, and the resulting fiber is false-twisted using a friction twisting apparatus, while being drawn simultaneously.
 7. The method as set forth in claim 6, wherein the side-by-side fiber prepared at a spinning speed of 1,500-4,000 m/min is false twisted at a false twisting-draw ratio of 1.0-1.5, a false twisting temperature of 100-180° C. and a draw-false twist processing speed of below 1,000 m/min using a false twisting apparatus.
 8. A polytrimethylene terephtalate conjugate fiber comprising two types of polytrimethylene terephtalates having different intrinsic viscosities in which a difference between the intrinsic viscosities ranges from 0.05 to 0.15, and having a side-by-side structure.
 9. The polytrimethylene terephtalate conjugate fiber as set forth in claim 8, wherein the conjugate fiber has high crimpability, with a strength of 2.0-3.5 g/den, an elongation of 30-65%, and a crimping rate of over 20%.
 10. The polytrimethylene terephtalate conjugate fiber as set forth in claim 8, wherein the conjugate fiber has high crimpability, with an elastic recovery of over 90% at an elongation of 30%. 